Abstract: The mysterious "calling drip" phenomenon that a series of clearly audible drip-like sounds could be heard at the top of stone steps after a footstep at the bottom, appearing at Crane Mountain in Qingdao has drawn attentions of tourists and acousticians in the past years. In this paper, we attempt to reveal the physical mechanism of "calling drip" by following the acoustic impedance of the periodic rigid surface. Under the quasi-plane wave approximation of low frequency, the numerical solution to the acoustic impedance of a single periodic stone step is obtained by using the transfer impedance function. At low frequency, the acoustic impedance of stone steps' surface presents pure acoustic reactance, which supports the existence of surface waves. And the finite element simulation is consistent with the theoretical analysis. Experiments are designed and performed by using the properties of surface waves. The analysis results of the experimental data show that, only the low-frequency part of sound energy is greatly preserved when the footstep at the bottom or the pulse along the surface of stone steps reaches the top, which is consistent with the theoretical analysis and simulation. In the end, we determine that it is the surface wave filtering effect of periodic steps makes the footstep change into a melodious drip-like sound.